Over the past year, two studies have been published. The first examined the mechanism by which fluid perfusing the distal portion of the renal tubule influenced a control over the rate of filtration. The results of these studies indicated that the calcium content of the distal perfusion fluid plays an initial role in this process. The second study examined the influence of the renal vasoconstrictor effects of chlorothiazide on its diuretic potency and also on its site of action within the nephron. It was learned that chlorothiazide does effect proximal sodium reabsorption; however, this effect is offset by its tendency to produce renal vasoconstriction and and a fall in GFR.